The present disclosure pertains to novel diagnostic assays for the diagnosis of amyloidosis, a group of disorders and abnormalities associated with amyloid protein such as Alzheimer's disease and related aspects. In particular, an antibody assay is provided.
Amyloidosis is not a single disease entity but rather a diverse group of progressive disease processes characterized by extracellular tissue deposits of a waxy, starch-like protein called amyloid, which accumulates in one or more organs or body systems. As the amyloid deposits accumulate, they begin to interfere with the normal function of the organ or body system. There are at least 15 different types of amyloidosis. The major forms are primary amyloidosis without known antecedent, secondary amyloidosis following some other condition, and hereditary amyloidosis.
Secondary amyloidosis occurs during chronic infection or inflammatory disease, such as tuberculosis, a bacterial infection called familial Mediterranean fever, bone infections (osteomyelitis), rheumatoid arthritis, inflammation of the small intestine (granulomatous ileitis), Hodgkin's disease and leprosy.
Amyloid deposits include amyloid P (pentagonal) component (AP), a glycoprotein related to normal serum amyloid P (SAP), and sulphated glycosaminoglycans (GAG), complex carbohydrates of connective tissue. Amyloid protein fibrils, which account for about 90% of the amyloid material, comprise one of several different types of proteins. These proteins are capable of folding into so-called “beta-pleated” sheet fibrils, a unique protein configuration which exhibits binding sites for Congo red resulting in the unique staining properties of the amyloid protein.
Many diseases of aging are based on or associated with amyloid-like proteins and are characterized, in part, by the buildup of extracellular deposits of amyloid or amyloid-like material that contribute to the pathogenesis, as well as the progression of the disease. These diseases include, but are not limited to, neurological disorders such as mild cognitive impairment (MCI), Alzheimer's disease (AD), like for instance sporadic Alzheimer's disease (SAD) or Familial Alzheimer's dementias (FAD) like Familial British Dementia (FBD) and Familial Danish Dementia (FDD), neurodegeneration in Down Syndrome, Lewy body dementia, hereditary cerebral hemorrhage with amyloidosis (Dutch type); the Guam Parkinson-Dementia complex. Other diseases which are based on or associated with amyloid-like proteins are progressive supranuclear palsy, multiple sclerosis; Creutzfeld Jacob disease, Parkinson's disease, HIV-related dementia, ALS (amyotropic lateral sclerosis), Adult Onset Diabetes; senile cardiac amyloidosis; endocrine tumors, and others, including macular degeneration.
Although pathogenesis of these diseases may be diverse, their characteristic deposits often contain many shared molecular constituents. To a significant degree, this may be attributable to the local activation of pro-inflammatory pathways thereby leading to the concurrent deposition of activated complement components, acute phase reactants, immune modulators, and other inflammatory mediators (McGeer et al., Tohoku J Exp Med. 174(3): 269-277 (1994)).
Recently, accumulating evidence demonstrates involvement of N-terminal modified Aβ peptide variants in Alzheimer's disease. Aiming biopsies display a presence of Aβ 1-40 and Aβ 1-42 not only in the brain of Alzheimer's patients but also in senile plaques of unaffected individuals. However, N-terminal truncated and pyroGlu modified Aβ N3pE-40/Aβ N3pE-42 is almost exclusively engrained within plaques of Alzheimer's disease patients, making this Aβ variant an eligible diagnostic marker and a potential target for drug development.
At present, several commercial manufacturers offer ELISA kits which allow a detection of Aβ 1-40/1-42 and Aβ N3pE-40/Aβ N3pE-42 in the low picogram (pg) range.
The brains of Alzheimer's disease (AD) patients are morphologically characterized by the presence of neurofibrillary tangles and by deposits of Aβ peptides in neocortical brain structures (Selkoe, D. J. & Schenk, D. Alzheimer's disease: molecular understanding predicts amyloid-based therapeutics. Annu. Rev. Pharmacol. Toxicol. 43, 545-584 (2003)). Aβ peptides are liberated from the amyloid precursor protein (APP) after sequential cleavage by β- and γ-secretase. The γ-secretase cleavage results in the generation of Aβ 1-40 and Aβ 1-42 peptides, which differ in their C-termini and exhibit different potencies of aggregation, fibril formation and neurotoxicity (Shin, R. W. et al. Amyloid beta-protein (Abeta) 1-40 but not Abeta 1-42 contributes to the experimental formation of Alzheimer disease amyloid fibrils in rat brain. J. Neurosci. 17, 8187-8193 (1997); Iwatsubo, T. et al. Visualization of Abeta 42(43) and Abeta 40 in senile plaques with end-specific Abeta monoclonals: evidence that an initially deposited species is Abeta 42(43). Neuron 13, 45-53 (1994); Iwatsubo, T., Mann, D. M., Odaka, A., Suzuki, N. & Ihara, Y. Amyloid beta protein (Abeta) deposition: Abeta 42(43) precedes Abeta 40 in Down syndrome. Ann. Neurol. 37, 294-299 (1995); Hardy, J. A. & Higgins, G. A. Alzheimer's disease: the amyloid cascade hypothesis. Science 256, 184-185 (1992); Roβner, S., Ueberham, U., Schliebs, R., Perez-Polo, J. R. & Bigl, V. The regulation of amyloid precursor protein metabolism by cholinergic mechanisms and neurotrophin receptor signaling. Prog. Neurobiol. 56, 541-569 (1998)).
The majority of Aβ peptides deposited in diffuse plaques are N-terminal truncated or modified. Studies of Piccini and Saido have shown that the core structure of senile plaques and vascular deposits consist of 50% pyroglutamate (pyroGlu) modified peptides (Piccini et al., J Biol Chem. 2005 Oct. 7; 280(40):34186-92; Saido et al., Neuron. 1995 February; 14(2): 457-66). PyroGlu modified peptides are more strongly cytotoxic than other Aβ species and stable against aminopeptidases (Russo et al., J Neurochem. 2002 September; 82(6):1480-9). Thus, pyroGluAβ species have a longer half life whereby the accumulation of these species and the formation of neurotoxic oligomers as well as aggregates are beneficial (Saido, Neurobiol Aging. 1998 January-February; 19(1 Suppl):S69-75). Due to the cyclization of glutamate to pyroGlu, charged amino acids will be lost which strongly reduces the solubility of the peptide and causes an increased aggregation tendency. In vitro studies have shown that the initial oligomerisation of e.g. Aβ3(pE) is much faster compared to non-modified peptides (Schilling et al., Biochemistry. 2006 Oct. 17; 45(41):12393-9).
Studies conducted by the Applicants have showed that Aβ11(pE) has a higher aggregation potency and a much lower solubility than Aβ3(pE). The group of Näslund J. et al. (Proc. Natl. Acad. Sci. Neurobiology, Vol. 91 pp. 8378-8382) detected by mass spectrometry the most prominent truncated variant AβpE(11-42) in brains of sporadic AD. Up to now the study of Näslund J. et al. is one of the few studies that examined the deposition of Aβ11(pE) in plaques.
All facts suggest that pyroGlu Aβ is a kind of germ for the initialization of fibril formation. In a new study (Piccini et al., 2005, supra) volunteers with plaque depositions but without AD specific pathology could be distinguished from AD patients due to the characteristic amount of Aβ-species. Thereby the amount of N-terminal truncated, pyroGlu modified peptides was significant higher in the brain of AD patients.
The posttranslational formation of pyroGlu at position 3 or 11 of Aβ-peptide implies cyclization of an N-terminal glutamate residue. Glutaminyl cyclase (QC) plays an important role in the generation of pyroGlu peptides. QC is wide-spread in the plant- and animal kingdom and inter alia, is involved in the maturation of peptide hormones. Both the cyclisation of glutamine by release of ammonia and of glutamate by release of water to pyroGlu is performed by QC. In contrast to the glutamine cyclization the glutamate cyclisation occurs not spontaneously. QC catalyses the efficient (unwanted) side reaction from glutamate to pyroGlu. The generated pyroGlu residue protects the protein against proteolytic degradation. There are several references which shows that QC plays an important role in the generation of pyroGlu Aβ:
1. In several studies it was shown that QC catalyses the formation of pyroGlu residues from glutamate at N-terminus of Aβ (Cynis et al., Biochim Biophys Acta. 2006 October; 1764(10):1618-25, Schilling et al., FEBS Lett. 2004 Apr. 9; 563(1-3):191-6);
2. Both Aβ peptides and QC are expressed in large quantities in hippocampus and cortex. These brain areas are at particular risk in AD (Pohl et al., Proc Natl Acad Sci USA. 1991 Nov. 15; 88(22):10059-63, Selkoe, Physiol Rev. 2001 April; 81(2):741-66);
3. The APP is cleaved by β-secretase during the transport to the plasma membrane whereby the N-terminus of Aβ with the free glutamate residue can be produced (Greenfield et al., Proc Natl Acad Sci USA. 1999 Jan. 19; 96(2):742-7). In the secretory vesicles a co-localisation of processed APP and the QC was determined. So in the mild acid milieu of the vesicles an accelerated modification of glutamate residue to pyroglutamatecan occur.
4. Also other neurodegeneratuve disease's (familiar Danish (FDD) or British dementia (FBD)) are related with N-terminal pyroGlu modified peptides e.g. Bri2, but in contrast they are not related to Aβ in terms of their primary structure (Vidal R. et al., 1999 Proc. Natl. Acad. Sci. U.S.A. 97, 4920-4925).
Possibly the QC-catalysed formation of pyroGlu Aβ is involved in the development and progression of neurodegenerative diseases. The formation of N-terminal modified amyloid peptides certainly represents a fundamental factor in the process of Aβ aggregation and could be the onset of disease. The suppression of the pyroGlu Aβ formation by inhibition of QC, might represent a therapeutic approach. QC inhibitors would be able to prevent the formation of pyroGlu Aβ, reduce the concentration of pyroglutamate Aβ in the brain and so delay the oligomerisation of Aβ-peptides. Schilling et al. show, that QC expression was up regulated in the cortex of Aβ patients and correlated with the appearance of pyroGlu-modified Aβ-peptide. Oral application of a QC inhibitor resulted in reduced pyroglutamate modified AβpE(3-42) level in two different transgenic mouse models of AD and in a new Drosophila model (Schilling et al., 2008 Biol. Chem. (389), 983-991).
Lewy body dementia (LBD) is a neurodegenerative disorder that can occur in persons older than 65 years of age, and typically causes symptoms of cognitive (thinking) impairment and abnormal behavioral changes. Symptoms can include cognitive impairment, neurological signs, sleep disorder, and autonomic failure. Cognitive impairment is the presenting feature of LBD in most cases. Patients have recurrent episodes of confusion that progressively worsen. The fluctuation in cognitive ability is often associated with shifting degrees of attention and alertness. Cognitive impairment and fluctuations of thinking may vary over minutes, hours, or days. Lewy bodies are formed from phosphorylated and nonphosphorylated neurofilament proteins; they contain the synaptic protein alpha-synuclein as well as ubiquitin, which is involved in the elimination of damaged or abnormal proteins. In addition to Lewy Bodies, Lewy neurites, which are inclusion bodies in the cell processes of the nerve cells, may also be present. Amyloid plaques may form in the brains of patients afflicted with DLB, however they tend to be fewer in number than seen in patients with Alzheimer's disease. Neurofibrillary tangles, the other micropathological hallmark of AD, are not a main characteristic of LBD but are frequently present in addition to amyloid plaques.
Amyotrophic lateral sclerosis (ALS) is characterized by degeneration of upper and lower motor neurons. In some ALS patients, dementia or aphasia may be present (ALS-D). The dementia is most commonly a frontotemporal dementia (FTD), and many of these cases have ubiquitin-positive, tau-negative inclusions in neurons of the dentate gyrus and superficial layers of the frontal and temporal lobes.
Inclusion-body myositis (IBM) is a crippling disease usually found in people over age 50, in which muscle fibers develop inflammation and begin to atrophy—but in which the brain is spared and patients retain their full intellect. Two enzymes involved in the production of amyloid-β protein were found to be increased inside the muscle cells of patients with this most common, progressive muscle disease of older people, in which amyloid-β is also increased.
Another disease that is based on or associated with the accumulation and deposit of amyloid-like protein is macular degeneration. Macular degeneration is a common eye disease that causes deterioration of the macula, which is the central area of the retina (the paper-thin tissue at the back of the eye where light-sensitive cells send visual signals to the brain). Sharp, clear, “straight ahead” vision is processed by the macula. Damage to the macula results in the development of blind spots and blurred or distorted vision. Age-related macular degeneration (AMD) is a major cause of visual impairment in the United States and for people over age 65 it is the leading cause of legal blindness among Caucasians. Approximately 1.8 million Americans of age 40 and older have advanced AMD, and another 7.3 million people with intermediate AMD are at substantial risk for vision loss. The government estimates that by 2020 there will be 2.9 million people with advanced AMD. Victims of AMD are often surprised and frustrated to find out how little is known about the causes and treatment of this blinding condition.
There are two forms of macular degeneration: dry macular degeneration and wet macular degeneration. The dry form, in which the cells of the macula slowly begin to break down, is diagnosed in 85 percent of macular degeneration cases. Both eyes are usually affected by dry AMD, although one eye can lose vision while the other eye remains unaffected. Drusen, which are yellow deposits under the retina, are common early signs of dry AMD. The risk of developing advanced dry AMD or wet AMD increases as the number or size of the drusen increases. It is possible for dry AMD to advance and cause loss of vision without turning into the wet form of the disease; however, it is also possible for early-stage dry AMD to suddenly change into the wet form.
The wet form, although it only accounts for 15 percent of the cases, results in 90 percent of the blindness, and is considered advanced AMD (there is no early or intermediate stage of wet AMD). Wet AMD is always preceded by the dry form of the disease. As the dry form worsens, some people begin to have abnormal blood vessels growing behind the macula. These vessels are very fragile and will leak fluid and blood (hence ‘wet’ macular degeneration), causing rapid damage to the macula.
The dry form of AMD will initially often cause slightly blurred vision. The center of vision in particular may then become blurred and this region grows larger as the disease progresses. No symptoms may be noticed if only one eye is affected. In wet AMD, straight lines may appear wavy and central vision loss can occur rapidly.
Diagnosis of macular degeneration typically involves a dilated eye exam, visual acuity test, and a viewing of the back of the eye using a procedure called fundoscopy to help diagnose AMD, and—if wet AMD is suspected—fluorescein angiography may also be performed. If dry AMD reaches the advanced stages, there is no current treatment to prevent vision loss. However, a specific high dose formula of antioxidants and zinc may delay or prevent intermediate AMD from progressing to the advanced stage. Macugen® (pegaptanib sodium injection), laser photocoagulation and photodynamic therapy can control the abnormal blood vessel growth and bleeding in the macula, which is helpful for some people who have wet AMD; however, vision that is already lost will not be restored by these techniques. If vision is already lost, low vision aids exist that can help improve the quality of life.
One of the earliest signs of age-related macular degeneration (AMD) is the accumulation of extracellular deposits known as drusen between the basal lamina of the retinal pigmented epithelium (RPE) and Bruch's membrane (BM). Recent studies conducted by Anderson et al. have confirmed that drusen contain amyloid beta. (Experimental Eye Research 78 (2004) 243-256).